My new Cobra - Problems

Hey guys, this is my first or second post on this forum, ive been lurking around for quite some time. Doing research on mods and repairs that are common, ive run into a situation.

I purchased a cobra in California 2003 46k miles - Silver. It seemed like the perfect deal

Subframe braced
kenne bell 2.4
BAP
Upgraded injectors
+.20 over and manley pistons

I went on a whim and purchased my dream car. towed the vehicle back from California to Arizona. Then boom, 37 miles after i purchased it. The engine started knocking, Just my luck.


Ive spent time pulling the motor and am in the process of rebuilding the short block ( see images) Essentially, the previous owner put cheap parts in the car, Siliconed every gasket and oring and put it up for sale.

Now on to my question. My engine builder is extremely knowledgable on the Modular ford motors, but the cylinder head is a different story, i have 2 places in my driver's side cylinder head that are a red flag to me, the previous owner had done the spark plug inserts on 2 cylinders.

See damage pictures




I plan on having the cylinder heads pressure tested, but im concerned about long term. What are your guys' thoughts on this, what would you guys do if it was your cylinder heads on a fresh bottom end?

I'd scrap the heads, used heads arent real expensive and it would give you a chance to upgrade to 9 thread spark plugs.

With the fresh bottom end and knowing those heads have been patched, I’d scrap them as well. Start fresh with some 9 thread heads, DB or DCs from an
Aviator. It would drive me insane and I’d be freaking out over every tiny noise or when I went into boost. I’d change them out just for the peace of mind. Did you go with a factory rebuild? Did you change the compression? Thinking about doing cams or anything since it’s apart? Look into the passenger secondary tensioners that’s flipped around to apply tension on the proper side.


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Sorry you got hosed, I’d scrap those heads

Fyi there's a guy on Facebook with 10 new 05 aviator crate motors for sale. He was parting out a couple and selling the DC heads for like $1300 a pair. Probably hard to beat that deal for a brand new set of heads.

Thanks for all the replies guys, budget is kinda where im going, after spending all of my savings on the cobra, doing the engine rebuild is really hitting the GUT and the bank account. I am pretty successful but still young (25).

the build we are currently going for is +.030 over and diamond racing pistons, leaving the stock style rods and crank. Our goal is 18psi and around 550whp. I can absolutely look into the option of new/used cylinder heads, the few ive seen have the upgraded plug threads but seem to have damage on the firing ports. (outside of the valve area)

roy_1031 said:

With the fresh bottom end and knowing those heads have been patched, I’d scrap them as well. Start fresh with some 9 thread heads, DB or DCs from an
Aviator. It would drive me insane and I’d be freaking out over every tiny noise or when I went into boost. I’d change them out just for the peace of mind. Did you go with a factory rebuild? Did you change the compression? Thinking about doing cams or anything since it’s apart? Look into the passenger secondary tensioners that’s flipped around to apply tension on the proper side.


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do you have a link to that tensioner setup? i have not seen that in any of the DIY / engine build stuff on here.

Withinshadows said:

the build we are currently going for is +.030 over

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is there a reason for going 30 over? Ie damage to the block and you have to? Outside of something like that there is no reason to overbore these engines. Its not like the 5.4 2valve where guys do it to unshroud bigger valves

DSG2003Mach1 said:

is there a reason for going 30 over? Ie damage to the block and you have to? Outside of something like that there is no reason to overbore these engines. Its not like the 5.4 2valve where guys do it to unshroud bigger valves

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the motor was already +.020 over, cylinder five (see image) has deep scoring in the walls, requiring machine work..

Withinshadows said:

the motor was already +.020 over, cylinder five (see image) has deep scoring in the walls, requiring machine work..

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id be tempted to just get another iron block or even go aluminum and start over vs what the **** ever that block has been through

DSG2003Mach1 said:

id be tempted to just get another iron block or even go aluminum and start over vs what the **** ever that block has been through

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that is definatly an option, the builder is AMP (all mustang preformance) here in AZ, he said any more than +.030 and he doesn't feel comfortable building it passed .030. We may be buying a block

Withinshadows said:

that is definatly an option, the builder is AMP (all mustang preformance) here in AZ, he said any more than +.030 and he doesn't feel comfortable building it passed .030. We may be buying a block

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if anything else happens to this current block - you're pretty much screwed

DSG2003Mach1 said:

if anything else happens to this current block - you're pretty much screwed

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Well, if it failed, i would be rebuilding again anyway right? i have seen some guys on here going +.040 with no issues too

Withinshadows said:

Well, if it failed, i would be rebuilding again anyway right? i have seen some guys on here going +.040 with no issues too

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if you hurt an individual cylinder you may or may not be able to repair it then youve pretty much lost all $ spent on other block work. I dunno how much power you're ultimately trying to make either though

Kind of off topic, but Chandler, AZ huh? I was just there last week.

What's the Mustang scene like there? I didn't see any Mustangs while I was out, but heard a few ripping down Chandler BLVD by the Fashion Mall...……..

Withinshadows said:

do you have a link to that tensioner setup? i have not seen that in any of the DIY / engine build stuff on here.

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Cobra Engineering LLC

Passenger Side Billet secondary Tensioner 4V DOHC Cobra / GT500 [444036] - $189.99 : Modular Motorsports, Home of the Worlds Fastest Modular Engines

Tensioner Only 4.6L - 5.4L - 5.8L - Ford - Passenger Side

The cobra engineering is the cheapest option if you’re on a budget. I think it reuses the parts from your factory tensioner. The MMR and Accufab are billet options.



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